Safety toe cap made from nano composite material and preparation method of nano composite safety toe cap

ABSTRACT

Safety toe caps made from nano composite material are made from multi-layers of laminated glass fiber cloth coated with resin paste, wherein the percentage ratio of the resin paste to the glass fiber cloth is as follows: the resin paste accounts for 30-45%, the glass fiber cloth accounts for 55-70%, and the total sum is 100%; the resin paste comprises the following components in percentage by mass: 30-50% of thermosetting resin, 0.1-5% of modified carbon nanotubes, 10-30% of modified nitrile rubber, 5-25% of polyurethaneacrylate, 1-5% of prepolymerized silane oligomer, 0.5-2% of initiator A (tert-Butyl peroxybenzoate), 1-2% of initiator medium temperature initiator B (tert-Butyl peroxy-2-ethylhexanoate), 5-20% of low-profile additive, 1-10% of toughening agent thickener A, 1-3% of toughening agent thickener B and 2-5% of inner demolding agent.

BACKGROUND

(i) Technical Field

The invention relates to the technical field of safety toe cap production, and in particular relates to safety toe caps made from a nano composite material and a preparation method of the toe caps.

(ii) Related Art

At present, the safety toe caps made from a thermosetting composite material are used more and more widely in industry, for example, in the Chinese patent No. CN2742806Y of the applicant, the safety toe caps are made by arranging and pressing multi-layers of continuous long fiber woven cloth which was pre-wetting by thermosetting resin in a specific direction, and results shows that the mechanical properties, such as the pressure resistance and the impact resistance, of the safety toe caps are much better than that of a safety toe caps which are formed by thermal plastic injection method or made from a short-fiber reinforcing thermosetting composite material (BMC). However, as different countries of the world continuously upgrade the safety testing standards, to achieve the safety requirements, safety toe caps made from the thermosetting/long-glass fiber reinforcing composite material need to be made into a certain thickness.

After 2008, because of the outburst of financial crisis and European debt crisis, economic recession happened all around the world and particularly in Europe and America, the purchasing power was obviously reduced, people generally have the thought of buying one less pair of shoes, however, the conventional safety shoes (boots) are heavy in weight and less in function, so that the market has urgent demands on multifunctional safety shoes. When the safety toe caps are put into ordinary leisure shoes, sports shoes and outdoor shoes, the shoes are suitable for both working and living, and then people can buy less one pair of shoes, the money is saved and the shoes can wear more conveniently; the multifunctional safety shoes become the inexorable trend in the future, and to achieve the requirements on the appearance design, the multifunctional safety shoes urgently need safety toe caps which are very thin in thickness and light in weight; however, the conventional safety toe caps made from the composite material are still too thick and cannot meet the design requirement. How to further improve the pressure resistance and the impact resistance of the composite material to a great extent so as to manufacture the safety toe caps made from the composite material which is thin and light becomes a problem which needs to be solved immediately.

CONTENT OF THE INVENTION

This invention is an improvement scheme of the patent of the publication patent number CN2742806Y, and aims at providing a nano composite material safety toe caps which are high in pressure resistance, high in impact resistance, light in weight and thin in wall thickness, for solving the technical problems that the safety toe caps are too large in thickness, heavy in weight and cannot meet the requirements of the novel multifunctional safety toe caps on appearance design and light weight.

The invention further provides a preparation method of the safety toe caps made from the nano composite material.

The invention adopts the following technical scheme for solving the technical problems:

The invention discloses safety toe caps made from nano composite material and a preparation method of the toe caps. The toe caps is made from a plurality layers of glass fiber cloth coated with resin paste, wherein the percentage ratio of the resin paste to the glass fiber cloth is as follows: the resin paste accounts for 30-45%, the glass fiber cloth accounts for 55-70%, and the total sum is 100%; the resin paste comprises the following components in percentage by mass: 30-50% of thermosetting resin, 0.1-5% of modified carbon nanotubes, 10-30% of modified nitrile rubber, 5-25% of polyurethaneacrylate, 1-5% of prepolymerized silane oligomer, 0.5-2% of high temperature initiator (tert-Butyl peroxybenzoate), 1-2% of medium temperature initiator (tert-Butyl peroxy-2-ethylhexanoate), 5-20% of low low-profile additive, 1-10% of thickener A, 1-3% of thickener B and 2-5% of inner demolding agent.

Preferably, the glass fiber cloth is a piece of silane modified alkali-free glass fiber cloth (warp yarns and weft yarns which are interleaved). A sizing procedure is performed. The silane coupling agent is coated on the surface of the glass fiber cloth. The coupling agent could react with the silanol group on the surface of the glass fiber cloth, linked by covalent bond, the surface of the glass fiber cloth had attached with unsaturated functional group which can react with the resin after the sizing process.

Preferably, the method for preparing the silane modified alkali-free glass fiber cloth the following steps: immersing the alkali-free glass fiber cloth into ethanol solution of silane coupling agent with the mass concentration of 3-8%, keeping for 10-20 seconds at 20-25° C., subsequently taking out the alkali-free glass fiber cloth, and drying for 10-12 hours in nitrogen at 90-110° C.

Preferably, the thermosetting resin is a bisphenol A epoxy based vinyl ester resin; the initiator A is tert-Butyl peroxybenzoate, the initiator B is tert-Butyl peroxy-2-ethylhexanoate, the low-profile additive is polycaprolactone, the thickener A is magnesium oxide, the thickener B is magnesium Magnesium hydroxide, and the inner demolding agent is stearic acid zinc.

Preferably, the preparation method of the modified carbon nanotubes comprises the following steps:

(1) firstly, making the carbon nanotubes into a plate shape (to avoid the contamination inside the chamber) with the thickness of 0.5-1 mm and the diameter of 0.5-5 cm, and immersed into plasma to react for 300-1,200 seconds to obtain an oxidized carbon nanotubes;

(2) adding the oxidized carbon nanotubes into a mixture of 95 wt % ethanol and silane coupling agent, which are mixed according to a weight ratio of 50:(1-10), and than adding hydrochloric acid to regulate the pH value to be 2.5-5.5, heating for 3-6 hours at 50-75° C., washing and filtering for 2-4 times by using ethanolanhydrous ethanol, and subsequently placed into a oven at 60-80° C. for 6-8 hours in nitrogen.

Preferably, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the diameter of the carbon nanotubes is 10-90 nanometers; the length is 5-50 micrometers.

Preferably, the constituting of plasma is argon with the purity of 99.995% and steam; the steam accounts for 0.5-5% of the volume percent of the raw material; the frequency of the radio-frequency for generating the plasma is 13.56 MHz; the R-F power of plasma generator is 100-250 W.

Preferably, the preparation method of the modified nitrile rubber comprises the following steps:

(1) in parts by weight, uniformly mixing 5-10 parts of methyl acrylic monomer, 50-60 parts of butadiene and 10-40 parts of acrylonitrile into a mixture liquid, further adding azodiisobutyronitrile (AIBN) which accounts for 0.5-2% of the weight of the mixture liquid and tert-dodecylthiol (with the CAS number of 25103-58-6, as a molecular weight regulator) which accounts for 0.1-1% of the weight of the mixture liquid, introducing nitrogen, subsequently continuously stirring, heating to be 50-70° C., and reacting for 2-5 hours at constant temperature so as to obtain carboxy-terminated butadiene-acrylonitrile (CTBN);

(2) in parts by weight, mixing 10-25 parts of carboxy-terminated butadiene-acrylonitrile, 100 parts of bisphenol A epoxy based vinyl ester resin, 15-25 parts of methacrylic acid and 1-2 parts of triphenylphosphine (TPP with the CAS number of 603-35-0), continuously stirring under nitrogen atmosphere, raising the temperature to be 100-150° C., keeping the temperature and reacting for 2-4 hours, and after the reaction, naturally cooling down to the room temperature.

Preferably, the preparation method of the prepolymerized silane oligomer comprises the following steps: in parts by weight, adding 1-3 parts of 95 wt % ethanol into 2-5 parts of silane coupling agent KH-570(CAS No.: 2530-85-0), continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 60-80° C., keeping the temperature and reacting for 2-5 hours, and finally depressurizing and distilling to remove ethanol solution.

A preparation method of the safety toe cap made from the nano composite material, comprising the following steps: uniformly mixing up components of the resin paste according to a specific ratio, subsequently uniformly coating the mixture on a single layer of glass fiber cloth, subsequently respectively covering a layer of PE film on the upper and lower surfaces of the glass fiber cloth coated with the resin paste covered with a layer of PE film for keeping the resin weight ratio, rolling through a roller to obtain a sheet material, aging for 20-28 hours at 35-45° C., cutting the prepreg, tearing off the PE films, stacking the cut prepreg into a pre-formed toe caps by using a hand lay-up method (stack 5-12 layers), further putting into a fixing mold on a hot-pressing machine, hot-pressing for 150-200 seconds (according to the thickness of a product) at the pressure of 30-45 MPa at 135-155° C. so as to form, demolding, subsequently grinding and trimming to obtain the product.

The safety toe caps in this patent are novel products that using the concept of nano material (modified carbon nanotubes) reinforcing into the safety toe caps for the first time in the world, after the nano reinforcing material is specially modified to satisfy the properties of the used resin, the strength and the toughness of the resin can be obviously improved, and thus using the nano composite material be used in a toe cap product.

The toughness of the resin is enhanced by using a plurality of special toughening agents and the modified carbon nanotubes, compared with the conventional manufacturing technique of the toe caps, the toughness and the safe inner height of the toe cap after been impacted are improved obviously, the toe caps can meet the safety testing standards of each countries only within small thickness. Once the thickness of the toe cap product is reduced, the weight of the toe caps has been obviously lighter at the same time, and the multiple purposes of being lighter and thinner are achieved.

The thermosetting resin used in the safety toe caps is a type of unsaturated polyester resin which with both the excellent property of epoxy resin and the rapid reaction rate of. The bisphenol A epoxy based vinyl ester resin is a type of the polyester resin, and the molecule structural formula is as follows:

wherein segment of bisphenol A on the molecular chain contains a structure of benzene ring on the skeleton which can provide stable chemical-resistant property, rigidity mechanical property and thermal stability, so that the product had high thermal resistant; the ether bond (—O—) on the skeleton had great chemical stability; the (—Ch3) methyl group has a good shielding effect due to stereo hindrance for protecting the ester group, enables the ester group to be hardly to hydrolyze (ester group (—COO—) is easy to be hydrolyzed by alkali and water), and improves the hydrolysis resistance; due to existence of hydroxyl group (—OH), so the wettability and the binding property of the resin are improved, the wetting effects between the resin and the glass fiber woven cloth are improved, and the glass fiber cloth can be completely wetted and sufficiently adhered to the resin so as to improve the Interlaminar shear strength of the toe cap product; the carbon-carbon double-bond structure (C═C) of the unsaturated olefin is positioned at the end part of the resin molecule chain which having high reaction activity group. It is easy to start up the cross-linking reaction and can obviously shorten the curing time of the resin phase, increase the curing degree of the resin, reducing the residual amount of the uncured monomer in the resin system at the same time, and further improve the corrosion resistance of the resin. Besides, as the cross-linking only happens at two ends of the molecule, the main molecular chain can be elongated under the stress action, so as to absorb external force or impact energy and improve the impact resistance of the resin.

As the bisphenol A epoxy based vinyl ester resin is prepared by polymerizing the epoxy resin and the unsaturated monoacid (methacrylic acid), the resin has the excellent properties both of the epoxy resin and the unsaturated polyester resin. In addition to excellent properties of mechanical strength, electric insulating property, water resistance, chemical resistance, high glass-transition temperature and thermal stability of the epoxy resin, the resin has excellent corrosion resistance and good industry operability—of the unsaturated polyester resin, for example, the viscosity of the resin is much lower than classic epoxy resin so that the operation is facilitated, and furthermore—the curing time can be appropriately adjusted because of the unsaturated group—at the end group of the resin structure.

To sum up, with multi-aspect advantages, the bisphenol A epoxy based vinyl ester resin is the good choice to be used as the resin substrate of the nano composite material.

Glass fiber cloth used in the present invention is not the general glass fiber cloth, but the alkali-free glass fiber cloth modified by silane, which can—generate covalent bond—between the silanol groups on silane coupling agent and the surface of glass fiber, make glass fiber surface carrying unsaturated functional groups —which can react with resin to form the covalent bonding between each other, increase the binding force of the interface glass fiber/resin, and realizing the mutual benefits of resin and fiber

The carbon nanotubes adopted in this invention are the single-walled carbon nanotubes or multi-walled carbon nanotubes that the diameter is tens of nanometers (10 to 90 nm), and length can be up to tens of microns (10 to 50 um), with an ultrahigh aspect ratio above 1000:1, the carbon nanotubes is extremely suitable for being used as reinforced material. As the nanometer material has the specific surface area (about 250 m²/g, and 15 times of general powdered graphite), the adopted carbon nanotubes can provide more effective area reacting with resin to enhance interface strength, as the carbon atom on carbon nanotubes has special arrangement structure, the carbon nanotubes is characterized in light weight (the density is only ⅓ of that of steel), high strength (5 times of that of steel), high toughness, flexibility, high elastic modulus and the like, which makes the carbon nanotubes can eliminate external force with a form of elastic deformation after being stressed, good recovery characteristics also exist after deformation, furthermore, rich in electron clouds on the carbon nanotubes stabilize the chemical properties, it is an ideal nano toughening-model reinforced material.

The modified carbon nanotubes are adopted in this invention to make the surface of carbon nanotubes to be functionalized, so as to remove the aggregation phenomenon of carbon nanotubes in the resin phase, and increasing the dispersity of the carbon nanotubes in resin phase, at the same time, to produce the capacity to form the covalent bond between CNT and resin base, thus developing strong binding strength—between organic/inorganic interface, when the composite is impacted by external force, the impact energy can be transferred to the carbon nanotubes which had stronger mechanical strength from resin base material which are weaker, and then dissipated the impact energy through the elastic deformation or distortion of the carbon nanotubes, thus achieving the great toughening and reinforcing effect. Therefore, the extremely-thin and light safety toe caps made from the nano composite material with higher strength can be produced.

The modified method of the carbon nanotubes is achieved by two steps, the first step is to perform plasma processing (oxidation treatment) on the surface of carbon nanotubes, and generate hydroxyl group (—OH) on the surface of CNTs. The second step is to—graft the functional groups which had the capacity to reacting with unsaturated groups on thermosetting resin to generate covalent bonding thereon by using the functional groups between the silane coupling agent and the hydroxyl group on the surface of carbon nanotubes.

In the first step, firstly, the carbon nanotubes are pressed into a plate shape with the thickness of 0.5-1 mm and the diameter of 0.5-5 cm, and placed into the location away about 1 to 5 mm from the plasma emission source in a reaction chamber to ensure that the CNTs can be fully soaked by the plasma for the oxidation reaction, the plasma source is prepared by mixing Ar with the purity of 99.995% and water vapor in a gas mixer in which the volume percent of the water vapor is 0.5 to 5%, the mixed gas enters the chamber to generate OH radical. The radio-frequency for producing plasma that the frequency is 13.56 MHz, and the power is 100 to 250 W, the plasma reaction time is 300 to 1200 seconds, finally the oxidation modification is completed.

Compared plasma oxidation method with conventional oxidation (carboxyl functionalizations) methods of carbon nanotube, the conventional well-known oxidation method of carbon nanotubes were usually usedstrong acid treatment, including—strong acid and high temperature treatment (>50° C.) to make the surface of carbon nanotube or ends be oxidized, thus to enable the carbon nanotubes to be grafted —COOH and —OH group on the surface of CNT, however, this method is easy to cause the problems that the carbon nanotubes are cut off in length or been eroded or peeled off on the surface structure, resulting in electrical property and mechanical property drop down, what's worse, for the environment, the acid waste liquid (and acid diluents) processed by strong acid is difficult to solve. The plasma oxidation process of the carbon nanotube—is the dry type process, during the process, there are no needed to add strong acid or any chemical solvent, only to feed inert gases and water vapor and generate plasma to make carbon nanotube been oxidization functionalized, which is fast, energy-saving, and an environmental green method.

The second step for the carbon nanotubes modification is as follows: adding the oxidized carbon nanotube into the mixture of 95% ethanol and silane coupling agent, adjusting ph to be 2.5 to 5.5 by adding hydrochloric acid, under the condition of nitrogen, heating for 3 to 6 h at 50 to 75° C., enabling the Si—OCHg on the silane coupling agent to be hydrolyzed into Si—OH in an aqueous environment, wherein the Si—OCHg can mutually have condensation reaction with the —OH on the surfaces of carbon nanotubes to make the silane coupling agent be connected with the surfaces of carbon nanotubes in a form of covalent bonding, after the reaction, washing the products with anhydrous ethanol for 2 to 4 times till the silane coupling agent on the non-grafted carbon nanotubes is cleaned up, after cleaning, putting into an oven for drying for 6 to 8 h under nitrogen atmosphere at 60 to 80° C., and then finishing the chemical modification of carbon nanotubes.

The silane coupling agent molecules produce the Si—OH after hydrolysis, and the carbon nanotubes produces —OH on the surfaces after oxidation treatment, and the Si—OH and —OH can start the condensation reaction to condensate with each other aftermixing with water molecule, which makes the Si—OH and —OH group on the CNT surface been connected within covalent bonding, and graft a new functional group to the carbon nanotubes, and this functional group can further react with resin, forming the covalent bonding between the carbon nanotubes and the resin, when material is impacted by external force which can be transferred into the carbon nanotubes with excellent mechanical properties from the resin which are weaker via such covalent bonding, and then the carbon nanotubes eliminate the external force via vibration, swing and similar spring-type recoverable deformations, such mechanism gives a stress dispassion capacity to whole materials, obviously improving the impact resistance of materials.

-   -   There are three types of toughening agent which are special for         the resin system comprises: modified nitrile rubber,         polyurethane acrylate, and pre-polymerized silane oligomers. The         toughening theory of each one is specified as follows:

1. Toughening mechanisms of modified nitrile rubber: an existing method is to toughen polyester resin by using nitrile rubber (NBR), the modified nitrile rubber is introduced into the polyester resin by using an alloying method, after the resin is cured, the rubber is distributed into the resin in small particles, the rubber particles in the resin can cause the effect of stress concentration when being impacted by external force, after the stress is greater than the yield stress of matrix, silver craze can be efficiently induced, and the production of the silver craze can absorb mass of impact energy and hinder the silver craze developing into crack, impact energy can also be consumed by the production of shear band, achieving significant toughening effect. But rubber cannot react with resin if there are no special chemical modification is performed to surface of rubber, which not only causes unsatisfactory toughening effect, but also causes other problems that the glass transition temperature (Tg) of the cured resin decreases seriously after rubber is added, and the like. Therefore, in order to be consistent with the curing conditions of the adopted heat convertible resin, according to the invention, the ‘methallyl group’ is used for modifying NBR, after grafting unsaturated end group to rubber, rubber could be the elastomer with unsaturated end group, capable of being bonded together with the resin by covalent bond, thus to produce powerful interface binding strength, and achieve the toughening effect. The nitrile rubber after modified by this invention has two characteristics: the first one is to make rubber owning reactive group capable of reacting with resin, to develop great covalent bond connection with resin after curing reaction, and is able to efficiently enhance the impact property of materials; the second one is that elastomer can be distributed evenly in main resin after being mixed to develop smaller rubber micro area, the compatibility between rubber and resin can be improved, and the stress can be evenly released while impacting, and the finer and more uniform dispersity of the modified NBR in resin can also effectively suppress the problem of phase separation, and obvious negative impact does not come up after toughening. According to the invention, the synthesis method of the modified NBR is as follows:

The modification of the adopted modified NBR is achieved by performing pre-condensation and other methods on carboxyl-terminated butadiene-acrylonitrile (CTBN) and epoxy resin, making the end of rubber molecules carrying unsaturated olefin group capable of reacting with main resin, developing strong binding between modified rubber and main resin, and evenly dispersing into resin after being modified due to polarity adjustment, which avoids the occurrence of phase separation and overall performance degradation. CTBN used for reacting with epoxy resin is powdery suspension which is obtained by the ternary copolymerization reaction between methacrylic acid monomer, butadiene, acrylonitrile and additives (peroxide initiator, azobisisobutyronitrile, AIBN), and tert-dodecyithiol (molecular weight regulator), after filtering the product CTBN, finishing the end carboxylation reaction for NBR. Acrylonitrile is added to NBR, thus improving strength and wear resistance, at the same time, the oil resistance, adhesive property, and ageing resistance performance for NBR are also enhanced.

And then, CTBN, epoxy resin, methacrylic acid and catalyst triphenylphosphine are mixed, nitrogen is introduced and the materials are continuously stirred for heat-preservation reaction, the multi-reaction is carried out at the same time, including the binding between CTBN and epoxy resin, binding between methacrylic acid and epoxy resin by condensation reaction, or binding between methacrylic acid and epoxy resin which already grafted with CTBN, the acid value after reaction should be less than 30 mg KOH/g, the materials are cooled to room temperature after reaction, and the BNR modification is accomplished.

By utilizing the CTBN, the present invention effectively improves the dispersity of modified rubber in resin phase (the polarity of modified rubber is adjusted by methacrylic acid to be similar to the structure of main resin), effectively improves the toughness of the material, and keeps the strength of the material away from decreasing due to the addition of rubber. The addition of BNR can also bring two effects of reducing resin shrinkage and strengthening material toughness.

2. polyurethaneacrylate (PUA) is oligomer of—acrylate with unsaturated olefin groups, and has good compatibility with resin,—can be evenly dispersed in the resin for increasing toughening —, PUA has urethane bond, and is characterized in that it is easy to form hydrogen bond between polymer molecules which are high binding affinity, after been impacted by external force, hydrogen bond can absorb the external energy by be cracked the hydrogen bond, convert, and hydrogen bond can be formed again after the external force had been removed, therefore, the cracking and re-generation of the hydrogen bond are reversible, which makes resin both have flexibility, high wear resistance, strong adhesion, excellent low temperature performance and high tear strength (higher than rubber) of polyurethane after been cured.

3. Prepolymerized silane oligomer: the silane coupling agent KH-570 after being pre-hydrolyzed and condensed is used in the present invention, KH-570 is the silane carrying three methoxyl groups and a methacryl functional group, the pretreatment of silane is firstly processed to hydrolyze the methoxy groups on the silane into silanol group, and then condensed with other silane molecular by silanol group on each silane molecule, after the hydrolysis and condensation step, the pre-polymerized silane coupling agent had the condensed Si—O—Si segments which had high flexibility and the methacryl functional group which can react with resin, after being mixed into resin and after the resin had been cured, the pre-condensed oligomer of silane can react with resin, and connect with each other by covalent bonding. When the resin is impacted by external force, mass interface bindings between resin and silane oligomer can transfer the stress from resin into the Si—O—Si segments of silane oligomer which are flexible and tough ( ) thus to achieve the purpose of effectively toughening. The modification time of the silane coupling agent needs to be controlled to adjust the silane oligomer compatibility in resin after hydrolysis and condensation, which can disperse the pre-polymerized silane oligomer into resin, so as to realize the toughening effect.

In order to promote the curing rate of the resin system the initiator used in the formula of the present invention is to mix the initiator A (tert-Butyl peroxybenzoate>high temperature initiator>CAS number:614-45-9) and initiator B (tert-Butyl peroxy-2-ethylhexanoate>medium temperature initiator>CAS number:3006-82-4)—for using. The curing reaction of resin is exothermic reaction, when the prepreg are added into a die, the heat is transferred from the die to the prepreg, but a certain temperature difference exists between the prepreg and the die, when the temperature of the prepreg rises to the temperature that the medium temperature initiator could be decomposit by heatand produce free radical—starts up the curing reaction of resin, increase the overall temperature of the prepregwhich needed for high temperature initiator (initiator A)(to be decomposited and start more curing reaction in short time, thus enhancing the curing rate of resin system and improving conversion of curing reaction to achieve the purpose of rapid curing.

The low-profile additive used in the invention is polycaprolactone, as the thermosetting resin has larger shrinkage (about 8-10%), the characteristic of the low-profile additive which the volume is similar to it is at high temperature while products are cooled, and when the temperature of resin drops down, the low-profile additive can keep the shape of resin which is shrunk because of cold, and can effectively prevent the resin from shrinkage, by adjustingthe the formula of resin system, the polycaprolactone can be uniformly dispersed in the resin, thus achieving the purpose of anti-shrinkage within uniform dispersity.

The thickening agent used in this invention is to pre-polymerize ( ) the resin sheets to a certain viscosity at 35 to 45° C., which is beneficial for the operation of hand lay-up method, and according to the invention, as the magnesium oxide and magnesium hydroxide which had higher activity than magnesium oxide are matched for using, the curing time can be shortened, which is faster than that of the traditional formula which only uses magnesium oxide, the viscosity of prepreg which required by hand lay-up method can be obtained only after about 20 to 28 h.

The internal demolding agent used in this present invention is zinc stearate, in addition to demolding, but also can make the surface of product can be bright and smooth, which is important influence on product appearance and the adhesion process in subsequent shoemaking processes is achieved.

Through the above technical scheme, the modified carbon nanotubes and a variety of toughening agents can be evenly dispersed into resin base materials, and covalent bonding with resin can be formed during the process of curing reaction, thus noticeable improving of the compressive strength and the impact strength of the composite, and furthermore preparing the ultra-light and ultra-thin novel safety toe caps made from the nano composite material.

1. Beneficial effects of the present invention are as follows:

2. The safety toe caps made from nano composite material have good compressive strength and impact strength, light weight and thin wall thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the profile SEM figure for single resin paste material samples,

In FIG. 1: (a) is the SEM figure of resin paste material in formula 2 for compared case; (b) is the SEM figure of resin paste material in formula 3 for compared case; (c) is the SEM figure of resin paste material in formula 4 for compared case;

FIG. 2 is the SEM figure for resin paste and glass fiber cloth composite samples.

FIG. 3 is the thickness comparison figure for existing safety toe caps and the one in this present invention.

SPECIFIC EMBODIMENTS

Specific specifications for the technical solution of the invention are as follows according to specific embodiments and combined with drawings.

In this invention, in addition to specific indication, the adopted materials, equipment and the like can be purchased from market or commonly used in this field. Methods in the following embodiments are the conventional methods in this field in addition to specific indication.

Embodiment 1 1. Raw Material Formula

The safety toe caps made from the nano composite material are composed of a plurality layers of glass fiber cloth coated with resin paste via laminating, mass percent of the resin paste and silane-modified alkali-free glass fiber cloth is as follows: 30% of resin paste, and 70% of alkali-free glass fiber cloth.

Counted by mass percent, the formula of resin paste is as follows: 50% of bisphenol A epoxy vinyl resin (commercially available), 0.1% of modified carbon nanotubes, 10% of modified nitrile rubber, 5% of urethane acrylate (commercially available), 5% of prepolymerized silane oligomers, 1% of initiator A (tert-Butyl peroxybenzoate) (commercially available), 2% of initiator B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 20% of low low-profile additive (polycaprolactone, commercially available), 1% of magnesium oxide, 2% of magnesium hydroxide, and 3.9% of zinc stearate.

1. The method for preparing silane-modified alkali-free glass fiber cloth is as follows: immersing alkali-free glass fiber cloth into silane coupling agent (KH570)-ethanol solution with the mass concentration of 3%, holding for 20 seconds at 20° C., and then taking out the alkali-free glass fiber cloth, baking for 12 hours under nitrogen atmosphere at 90° C.

2. The method for preparing modified carbon nanotubes is as follows:

(1) Firstly, pressing the carbon nanotubes into pie shape with the thickness of 0.5 mm and the diameter of 0.5 cm, immersing into plasma for reacting 1200 seconds to obtain oxidized carbon nanotubes.

Carbon nanotubes are the single-walled carbon nanotubes of which diameter is 10 nm and the length is 5 microns.

The raw material of plasma is the mixture of argon of which the purity is 99.995%, and water vapor, the water vapor accounts for 0.5%, the RF for producing plasma is 13.56 MHz, and the power is 100 W.

(2) Carbon nanotubes are added to the mixed liquor consisting of 95 wt % of ethanol and silane coupling agent (KH570) according to the weight ratio of 10:1, hydrochloric acid with the concentration of 1M is added to adjust pH to be 2.5, the carbon nanotubes are heated for 6 hours at 50° C. under the condition of nitrogen, washed twice with anhydrous ethanol, and then added to an oven for baking for 8 hours at 60° C. in the presence of nitrogen atmosphere.

3. The method for preparing modified nitrile rubber is as follows:

(1) In parts by weight, mixing 5 parts of methacrylic acid monomer, 50 parts of butadiene and 10 parts of acrylonitrile into a mixed solution, adding 0.5 wt % of azodiisobutyronitrile and 0.1 wt % of tert-dodecylthiol in the mixed solution, after introducing nitrogen, continuously stirring, and heating up to 50° C. for thermostatic reaction for 5 hours to obtain CTBN;

(2) In parts by weight, mixing 10 parts of CTBN, 100 parts of bisphenol A epoxy resin, 15 parts of methacrylic acid and 1 part of Triphenylphosphine as catalyst, continuously stirring under the condition of loading nitrogen, heating up to 100° C., and then reacting for 4 h, at the end of the reaction, naturally cooling to the room temperature.

4. The method for preparing prepolymerized silane oligomers is as follows: in parts by weight, adding 1 part of 95 wt % ethanol to 2 parts of silane coupling agent KH-570, continuously stirring under the condition of loading nitrogen, heating up to 60° C., and then performing thermal reaction for 5 hours, finally, removing the ethanol through reduced pressure distillation.

2. The preparation method of the safety toe caps made from the nano composite material, characterized by comprising the following steps: uniformly mixing up all components of the resin paste according to a ratio, subsequently uniformly coating the mixture on a single layer of glass fiber cloth, subsequently respectively covering a layer of PE film on the upper and lower surfaces of the glass fiber cloth coated with the resin paste, then rolling through a roller to obtain a sheet material, aging for 28 hours at 35° C., cutting the prepreg, tearing off the PE films, stacking the cut prepreg into the pre-formed toe caps by using the hand lay-up method (the present routine method), placing into the fixed mold on the thermal compressor, thermally pressing for 200 seconds under the pressure of 30 MPa and the temperature of 35° C. and molding, demolding, and subsequently grinding and trimming to obtain a product.

Embodiment 2 1. Raw Material Formula

The safety toe caps made from the nano composite material are made by press-fitting a plurality layers of laminated glass fiber cloth coated with resin paste, the percentage ratio of the resin paste to the glass fiber cloth is as follows: the resin paste accounts for 45%, and the silane-modified alkali-free glass fiber cloth accounts for 55%.

The resin paste comprises the following formula components in percentage by mass: 30% of bisphenol A vinyl ester resin (commercially available), 5% of modified nanotube, 30% of modified nitrile rubber, 5% of polyurethaneacrylate (commercially available), 2% of prepolymerized silane oligomer, 0.5% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1.5% of initiator B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 10% of low-profile additive (polycaprolactone, commercially available), 10% of magnesium oxide, 1% of Magnesium hydroxide and 5% of zinc stearate.

1. The preparation method of the silane-modified alkali-free glass fiber cloth is made by immersing a piece of alkali-free glass fiber cloth into ethanol solution of silane coupling agent (KH570) with the mass concentration of 8%, keeping for 10 seconds at 25° C., subsequently taking out the alkali-free glass fiber cloth, and drying for 10 hours in nitrogen at 110° C.

2. The preparation method of the modified carbon nanotube comprises the following steps:

(1) Firstly, making the carbon nanotubes into a piecake shape with the thickness of 1 mm and the diameter of 5 cm, and soaking into plasma to react for 550 seconds to obtain the oxidized carbon nanotubes.

The carbon nanotubes are multi-walled carbon nanotubes, wherein the diameter of the carbon nanotubes is 90 nanometers; the length thereof is 50 micrometers.

The raw material of plasma is a mixture of argon with the purity of 99.995% and steam, wherein the steam accounts for 2% of the volume percent of the raw material; the frequency of the radio-frequency for generating the plasma is 13.56 MHz; the power is 200 W.

(2) Adding the oxidized carbon nanotubes into 95 wt % of a mixture solution with ethanol and a silane coupling agent (KH570) which are mixed according to a weight ratio of 50:1, adding hydrochloric acid with concentration value of 1% to regulate the pH value to be 5.5, heating for 5 hours at 60° C., washing for 3 times by using ethanolanhydrous ethanol, and subsequently feeding into the oven for drying for 6 hours at 80° C. in nitrogen.

3. The preparation method of the modified nitrile rubber comprises the following steps:

(1) In parts by weight, uniformly mixing 10 parts of methyl acrylic monomer, 60 parts of butadiene and 30 parts of acrylonitrile into a mixture liquid, further adding azodiisobutyronitrile which accounts for 2% of the weight of the mixture liquid and tert-dodecylthiol which accounts for 1% of the weight of the mixture liquid, introducing nitrogen, subsequently continuously stirring, heating to be 70° C., and reacting for 2 hours at constant temperature so as to obtain carboxy-terminated butadiene-acrylonitrile;

(2) In parts by weight, mixing 25 parts of carboxy-terminated bufadiene-acrylonitrile, 100 parts of bisphenol A epoxy based vinyl ester resin, 20 parts of methacrylic acid and 2 parts of triphenyiphosphine, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 150° C., keeping the temperature and reacting for 2 to 4 hours, and after the reaction, naturally cooling down to be the room temperature.

4. The preparation method of the prepolymerized silane oligomer comprises the following steps: in parts by weight, adding 3 parts of 95 wt % ethanol into 5 parts of silane coupling agent KH-570, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 80° C., keeping the temperature and reacting for 2 hours, and finally depressurizing and distilling to remove ethanol.

2. The preparation method of the safety toe caps made from the nano composite material, characterized by comprising the following steps: uniformly mixing up all components of the resin paste according to a ratio, subsequently uniformly coating the mixture on a single layer of glass fiber cloth, subsequently respectively covering a layer of PE film on the upper and lower surfaces of the glass fiber cloth coated with the resin paste, then rolling through a roller to obtain a sheet material, aging for 20 hours at 45° C., cutting the prepreg, tearing off the PE films, stacking the cut prepreg into the pre-formed toe caps by using the hand lay-up method, placing into the fixed mold on the thermal compressor, thermally pressing for 150 seconds under the pressure of 45 MPa and the temperature of 155° C. and molding, demolding, and subsequently grinding and trimming to obtain the product.

Embodiment 3 1. Raw Material Formula

The safety toe caps made from the nano composite material are made by press-fitting a plurality layers of laminated glass fiber cloth coated with resin paste, the percentage ratio of the resin paste to the glass fiber cloth is as follows: the resin paste accounts for 40%, and the silane-modified alkali-free glass fiber cloth accounts for 60%.

The resin paste comprises the following formula components in percentage by mass: 30% of bisphenol A vinyl ester resin (commercially available), 3% of modified nanotubes, 25% of modified nitrile rubber, 25% of polyurethaneacrylate (commercially available), 1% of prepolymerized silane oligomer, 2% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1% of initiator B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 5% of low-profile additive (polycaprolactone, commercially available), 5% of magnesium oxide, 1% of magnesium hydroxide and 2% of zinc stearate.

1. The preparation method of the silane-modified alkali-free glass fiber cloth is made by immersing a piece of alkali-free glass fiber cloth into an ethanol solution of a silane coupling agent (KH570) with the mass concentration of 8%, keeping for 10 seconds at 25° C., subsequently taking out the alkali-free glass fiber cloth, and drying for 10 hours in nitrogen at 110° C.

2. The preparation method of the modified carbon nanotube comprises the following steps:

(1) Firstly, making the carbon nanotubes into a piecake shape with the thickness of 1 mm and the diameter of 2 cm, and soaking into plasma to react for 300 seconds to obtain the oxidized carbon nanotubes.

The carbon nanotubes are multi-walled carbon nanotubes, wherein the diameter of the carbon nanotubes is 90 nanometers; the length thereof is 50 micrometers.

The raw material of plasma is a mixture of argon with the purity of 99.995% and steam, wherein the steam accounts for 2% of the volume percent of the raw material; the frequency of the radio-frequency for generating the plasma is 13.56 MHz; the power is 250 W.

(2) Adding the oxidized carbon nanotubes into 95 wt % of a mixture solution with ethanol and a silane coupling agent (KH570) which are mixed according to a weight ratio of 5:1, adding hydrochloric acid with concentration value of 1M to regulate the pH value to be 3, heating for 3 hours at 75° C., washing for 4 times by using ethanolanhydrous ethanol, and subsequently feeding into the oven for drying for 6 hours at 80° C. in nitrogen.

3. The preparation method of the modified nitrile rubber comprises the following steps:

(1) In parts by weight, uniformly mixing 10 parts of methyl acrylic monomer, 55 parts of butadiene and 20 parts of acrylonitrile into a mixture liquid, further adding azodiisobutyronitrile which accounts for 1% of the weight of the mixture liquid and tert-dodecylthiol which accounts for 0.5% of the weight of the mixture liquid, introducing nitrogen, subsequently continuously stirring, heating to be 65° C., and reacting for 2 hours at constant temperature so as to obtain carboxy-terminated butadiene-acrylonitrile;

(2) In parts by weight, mixing 15 parts of carboxy-terminated butadiene-acrylonitrile, 100 parts of bisphenol A epoxy based vinyl ester resin, 25 parts of methacrylic acid and 1.5 parts of triphenylphosphine, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 120° C., keeping the temperature and reacting for 3 hours, and after the reaction, naturally cooling down to be the room temperature.

4. The preparation method of the prepolymerized silane oligomer comprises the following steps: in parts by weight, adding 1 part of 95 wt % ethanol into 3 parts of silane coupling agent KH-570, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 70° C., keeping the temperature and reacting for 3 hours, and finally depressurizing and distilling to remove ethanol.

2. The preparation method of the safety toe caps made from the nano composite material, characterized by comprising the following steps: uniformly mixing up all components of the resin paste according to a ratio, subsequently uniformly coating the mixture on a single layer of glass fiber cloth, subsequently respectively covering a layer of PE film on the upper and lower surfaces of the glass fiber cloth coated with the resin paste, then rolling through a roller to obtain a sheet material, aging for 20 hours at 35° C., cutting the prepreg, tearing off the PE films, stacking the cut prepreg into the pre-formed toe caps by using the hand lay-up method (the present routine method), placing into the fixed mold on the thermal compressor, thermally pressing for 150 seconds under the pressure of 45 MPa and the temperature of 155° C. and molding, demolding, and subsequently grinding and trimming to obtain the product.

Embodiment 4

1. Raw material formula: the safety toe caps made from the nano composite material are made by press-fitting a plurality layers of laminated glass fiber cloth coated with resin paste, the percentage ratio of the resin paste to the glass fiber cloth is as follows: the resin paste accounts for 40%, and the silane-modified alkali-free glass fiber cloth accounts for 60%.

The resin paste comprises the following formula components in percentage by mass:

30% of bisphenol A inyl ester resin (commercially available), 2% of modified nanotubes, 30% of modified nitrile rubber, 10% of polyurethaneacrylate (commercially available), 2% of prepolymerized silane oligomer, 2% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1% of initiator. B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 10% of low-profile additive (polycaprolactone, commercially available), 5% of magnesium oxide, 3% of Magnesium hydroxide and 5% of zinc stearate.

1. The preparation method of the silane-modified alkali-free glass fiber cloth is made by immersing a piece of alkali-free glass fiber cloth into ethanol solution of silane coupling agent (KH570) with the mass concentration of 5%, keeping for 15 seconds at 20° C., subsequently taking out the alkali-free glass fiber cloth, and drying for 11 hours in nitrogen at 100° C.

2. The preparation method of the modified carbon nanotube comprises the following steps:

(1) Firstly, making the carbon nanotubes into a piecake shape with the thickness of 0.5 mm and the diameter of 2 cm, and soaking into plasma to react for 720 seconds to obtain the oxidized carbon nanotubes.

The carbon nanotubes are multi-walled carbon nanotubes, wherein the diameter of the carbon nanotubes is 60 nanometers; the length thereof is 30 micrometers.

The raw material of plasma is a mixture of argon with the purity of 99.995% and steam, wherein the steam accounts for 1% of the volume percent of the raw material; the frequency of the radio-frequency for generating the plasma is 13.56 MHz; the power is 180 W.

(2) Adding the oxidized carbon nanotubes into 95 wt % of a mixture solution with ethanol and a silane coupling agent (KH570) which are mixed according to a weight ratio of 50:3, adding hydrochloric acid with concentration value of 1M to regulate the pH value to be 3, heating for 4 hours at 60° C., washing for 3 times by using ethanolanhydrous ethanol, and subsequently feeding into the oven for drying for 7 hours at 70° C. in nitrogen.

3. The preparation method of the modified nitrile rubber comprises the following steps:

(1) In parts by weight, uniformly mixing 10 parts of methyl acrylic monomer, 50 parts of butadiene and 40 parts of acrylonitrile into a mixture liquid, further adding azodiisobutyronitrile which accounts for 1% of the weight of the mixture liquid and tert-dodecylthiol which accounts for 0.5% of the weight of the mixture liquid, introducing nitrogen, subsequently continuously stirring, heating to be 60° C., and reacting for 3 hours at constant temperature so as to obtain carboxy-terminated butadiene-acrylonitrile;

(2) In parts by weight, mixing 25 parts of carboxy-terminated butadiene-acrylonitrile, 100 parts of bisphenol A epoxy based vinyl ester resin, 20 parts of methacrylic acid and 1 part of triphenylphosphine, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 120° C., keeping the temperature and reacting for 3 hours, and after the reaction, naturally cooling down to be the room temperature, and having the acid value less than 30 mg KOH/gafter reaction.

4. The preparation method of the prepolymerized silane oligomer comprises the following steps: in parts by weight, adding 3 parts of 95 wt % ethanol into 2 parts of silane coupling agent KH-570, continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 70° C., keeping the temperature and reacting for 3 hours, and finally depressurizing and distilling to remove ethanol.

2. The preparation method comprises the steps of uniformly mixing all components of the resin paste, and then uniformly coating the resin paste on a single glass fiber cloth, respectively covering a layer of PE film on the upper and lower surface of the glass fiber cloth coated with the resin paste, rolling to obtain a sheet material through a roller, curing the sheet material for 24 h at 40° C., cutting and shaping the prepreg, peeling off the PE film, folding the cut and shaped prepreg into preformed toe caps through a hand lay-up method (an existing conventional method), and then placing the toe caps into a fixed mold on a hot press so as to form the toe caps after thermally pressing for 180 seconds in the pressure of 40 MPa at 150° C., and demolding to obtain the product after grinding and trimming procedures.

Contrast Example 1

The difference of the contrast example 1 and the contrast 4 is the formula of the resin paste, and others are consistent to the same embodiment 4.

According to the mass percentage, the formula of the resin paste is as follows:

74% of bisphenol A epoxy based vinyl ester resin (commercially available), 2% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1% of initiator B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 10% of low-profile agent (polycaprolactone, commercially available), 5% of magnesium oxide, 3% of magnesium hydroxide, and 5% of zinc stearate.

Contrast Example 2

The difference of the contrast example and the contrast 4 is the formula of the resin paste, and others are consistent to the same implementation example 4.

According to the mass percentage, the formula of the resin paste is as follows:

32% of bisphenol A epoxy based vinyl ester resin (commercially available), 30% of modified nitrile rubber, 10% of polyurethaneacrylate (commercially available), 2% of pre-polymerized silane oligomer, 2% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1% of initiator B (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 10% of low-profile agent (polycaprolactonem commercially available), 5% of magnesium oxide, 3% of magnesium hydroxide, and 5% of zinc stearate.

Contrast Example 3

The difference of the contrast example and the contrast 4 is the formula of the resin paste, and others are consistent to the same implementation example 4.

According to the mass percentage, the formula of the resin paste is as follows:

30% of bisphenol A epoxy based vinyl ester resin (commercially available), 2% unmodified CNT, 30% of unmodified nitrile rubber, 10% of polyurethaneacrylate (commercially available), 2% of prepolymerized silane oligomer, 2% of initiator A (tert-Butyl peroxybenzoate, commercially available), 1% of medium-temperature initiator (tert-Butyl peroxy-2-ethylhexanoate, commercially available), 10% of low-profile agent (polycaprolactonem commercially available), 5% of magnesium oxide, 3% of magnesium hydroxide, and 5% of zinc stearate.

Performance Test

1. A high resolution scanning electron microscope (SEM) is utilized to characterise the cross-section of the cured resin samples which were added raw carbon nanotube (CNT), modified CNT and without any types of CNT, the FIG. 1( a) shows the cross-section of the cured resin samples which without CNT); observation shows that the broken resin generates homodromous broken lines, a broken surface is smooth and is provided with some stripes which been pulled out are about 1 micron in scale; FIG. 1( b) is the cross-section of the cured resin samples which within unmodified CNT, the plurality of aggregation of unmodified CNT can be obviously seen, so as to form an aggregation which is 5-10 um in scale; and in the resin around the aggregation, no carbon nanotubes exist, so that the dispersibility of the unmodified CNT in a resin substrate is vary poor, and the excellent property of the CNT can not be performed in the composite; FIG. 1 (c) is the cross-section of the resin which added with the modified CNT, the CNTs are uniformly dispersed in the resin substrate in nanoscale, the added modified CNT was grafted functional groups on the surfaces of the carbon nanotubes during the modification process, the aggregation effect of the carbon nanotubes can be effectively solved, and the carbon nanotubes are uniformly distributed in the resin substrate to form a fracture surfaces which are fine and coarse (generating silver crazes to absorb more energy), so that the better reinforcing effect can be achieved, and the stability and reliability of improving the strength of composite material can be improved simultaneously.

2. FIG. 2A shows the morphology of a cross-section sample of the resin and the glass fiber cloth composite material prepared according to the match ratio of the contrast sample 2, the FIG. 2B is the enlarged drawing of the FIG. 2A; and the FIG. 2C is the morphology of a cross-section sample of the resin paste and the glass fiber cloth composite material prepared according to the match ratio of the embodiment 4, the FIG. 2D is the enlarged drawing of the FIG. 2C. With view of the microstructures of the broken surfaces of samples which is not added with the CNT, the broken surface of the sample is smooth, and is not coarse (compare FIG. 2A and FIG. 2B); in the sample which is added with the modified CNT, the broken surface is filled with thin veins, and the fractured surfaces are fine and uniformly distributed, so that the fine fractured surface proves that the extension of the fractured surface of the sample is blocked by the uniformly distributed carbon nanotubes in the sample containing the carbon nanotubes due to the addition of the modified CNT when the material is broken, the fracture extension shall bypass the CNTs, and the carbon nanotubes are uniformly distributed; strong interface strength can be generated by a covalent bond bonding between the carbon nanotubes and the resin, so that more fractured veins show that the materials can absorb more impact energy and have stronger fracture resistance.

3. The CHARPY Impact Strength Test Result of Nanocomposite Samples.

The penetrating impact of the national standard-CHARPY impact experiment GB/T 1043.1-200 is adopted to test, 10-15 samples are prepared for testing every time, the obtained data is average value, seeing the table 1, and the ascent rate corresponds to the contrast example 1.

TABLE 1 Impact Rate of strength ascent Appearance (kJ/m2) (%) Contrast Orange and transparent 20.1 0.00 example 1 (Contrast value) Contrast Milky white and opaque 26.2 30.35 example 2 Contrast Black grey and opaque, with 22 9.45 example 3 fine sand black points embodiment Regular black without black 33.7 67.66 example 1 points embodiment Regular black without black 34 69.15 example 2 points embodiment Regular black without black 34.6 72.14 example 3 points embodiment Regular black without black 35.1 74.63 example 4 points

According to the result of the table 1, the impact strength of the pure resin paste is worst in the seven samples which is not added any toughening agent in the resin paste (contrast 1); the strength is improved by 30.35% after three types of toughening agents are added (contrast 2), the effect of the toughening agents is provided to be obvious, and the impact strength is enhanced; according to a series of experimental results of adding each types of carbon nanotubes in the resin as reinforcement, the impact strength of the formula added with the unmodified CNT (contrast 3) is worse than contrast 2 which adding without CNT, since the unmodified CNT has ultra-high surface area (>200 m̂2/g),(high surface area will result in high surface energy), and easily form aggregation (to reduce the surface energy by nature) in the resin, so that the aggregations are filled with the carbon tunes but lacks of the resin; after the resin is cured, the defects of the CNT aggregations are distributed everywhere in the resin, forming the crack in the resin as many defects, when the materials had been impacted by external stress and fracture will generate easier due to more defects in the materials when the materials had been impacted by external stress; in the experimental result (embodiments 1, 2, 3 and 4) added with the modified CNT, the impact strength of resin can be obviously enhanced, and is greater than the pure resin by about 60%, and greater than the resin added with the 3 toughening agents by about 30%, so that the modified CNT can not only overcome the problem of the aggregation of the carbon nanotubes, but also form strong covalent bond between the carbon nanotubes and the resin, is completely connected with the resin on the ultra-high surface area of the carbon nanotubes, and gives full play to the excellent performance to reinforce the impact strength of the resin.

4. The impact test result (the naked test of the toe caps) of the nanocomposite safety toe caps.

The toe caps prepared by the nanocomposite are subjected to material test according to a United States Standard (ASTM F2413-05 MI/75 C/75).

According to the United States Standard, the toe caps are directly placed on a test platform of a steel base (naked test), a hard clay with the diameter of phi 25+/−0.5 mm is placed inside the toe caps, and is centered to be tangent to an opening end, and then the toe caps are subjected to impact test, the impact head is cylindrical point impact, is phi 25+/−0.5 mm in diameter, 25 mm in cambered surface, and 60 mm in length. The impact energy is 102 J, and the inner safe height of the 8 yard toe cap is 15 mm according to the requirements of the inner height of the impacted toe caps (the height of the deepest sunken part of the impacted clay).

According to the standard of safety toe cap, the higher of the inner safe height of the impacted toe caps means the shock proof performance of the toe caps is better (under the condition that the top part of the toe caps is not fractured after the impact). After test, the materials of this invention can absorb more impact energy, and the test results are seen in the table 2.

TABLE 2 Experimental results of the naked test of the toe caps Sample No. Contrast 2 Contrast 3 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 1. 16.68 15.84 19.84 20.23 20.11 20.68 2. 16.44 15.63 19.69 15.87 20.03 20.34 3. 16.32 15.25 18.73 15.54 19.72 19.94 4. 16.38 15.1 18.68 19.27 19.52 19.52 15.88 14.66 18.56 18.56 19.25 19.63 6. 15.67 14.43 18.33 1S.53 18.78 18.95 7. 15.59 14.26 17.76 17.89 18.52 18.88 8. 15.53 14.22 17.54 17.71 18.28 18.68 Average 16.06 14.92 18.64 18.3 20.02 19.58 value (mm) Average 0.00 −7.08 16.06 18.30 20.02 21.83 rate of ascent (%) Minimum 15.53 14.22 17.54 17.71 18.28 18.68 value (mm) Standard 15 mm (naked test) Whether Nothing The light can pass Nothing Nothing Nothing Nothing the light the fracture of can pass the sample 5 and the fracture the sample 7 Whether Conformity Non-conformity Conformity Conformity Conformity Conformity results qualified

The calculation formula of the average rate of ascent is equal to [(the average values of all samples−the average value of the contrast 2)/the average value of the contrast 2]*100%.

According to the test result of the impacted toe caps in the table 2, after the toe caps are prepared by the formula (contrast 2) of adding three types of toughening agents in the resin, the testing value can pass the standard of United State, but it's closer to the standard value; in the formula (contrast 3) of adding the unmodified CNT in the resin, some of the toe caps which cannot pass the safety standard and light can pass through the fracture crack of impacted toe caps, so that the unmodified carbon nanotubes has negative influence after added into the resin, and some defect points of CNT aggregation in the resin are formed due to the addition of the unmodified carbon nanotubes, so that the material cannot effectively absorb the impact energy to easily result in fraction; the toe caps prepared by the formulas (embodiments 1-4) of adding the three types of toughening agents and the modified carbon nanotubes into the resin can pass the standard of United States, obviously exceed the standard values, and is higher than the contrast 2 by about 20%, so that the strength of the toe caps can be obviously enhanced due to the addition of the modified carbon nanotubes; on this basis, because of the strength of composite is enhanced, we can reduce the thickness of the top caps, the weight of the toe caps can be reduced when the thickness of the toe caps are reduced, therefore, we can prepare thinner and lighter nanocomposite safety toe caps which can pass the safe standard specifications of all countries.

5. Comparison for the Thicknesses of the Safety Nanocomposite Top Caps:

FIG. 3 is a comparison figure of the thickness of existing safety toe caps and the safety toe caps provided by the invention, wherein the left figure is the wall thickness of the existing safety toe caps, and the right figure is the wall thickness (light and thinner design) of the safety toe caps provided by the invention. According to the invention, the walls of the safety toe caps provided by the invention are thinner, data shows that the wall thickness of the safety toe caps provided by the invention is averagely reduced by about 1.5 mm (the thickest place of the wall thickness of the existing safety toe caps is about 6 mm), the weight is 78.9% of the existing safety toe cap, and the wall thickness of the safety toe caps provided by the invention is thinner, but the performance can still pass the test (see the table 3) of the United States standard (ASTM F2413-05 MI/75 C/75), and the data in the table 3 proves that the safety toe caps provided by the invention can pass the standard and realize triple targets of the safety toe caps of being stronger, thinner and lighter.

TABLE 3 Comparison for the naked measurement value of the safety toe caps (the same model and size) prepared by the formula of the embodiment 4 provided by the invention and the existing safety toe caps. Safety toe Existing caps provided safety Sample by the invention toe caps Average weight (S) 49.2 62.3 Thickest wall thickness 4.5 6.0 (mm) Result of impact test Sample 1. 20.68 16.85 Sample 2. 20.34 16.47 Sample 3. 19.94 16.42 Sample 4. 19.52 16.30 Sample 5. 19.63 16.27 Sample 6. 18.95 16.19 Sample 7. 18.88 16.15 Sample 8. 18.68 16.01 Average value (mm) 19.58 16.33 Minimal value (mm) 18.68 16.01 Standard (naked 15.00 15.00 measurement) (mm) Whether the light can Nothing Nothing pass the fracture Whether results qualified Conformity Conformity

6. Test Result of a Dynamic Mechanical Analysis Meter (DMA)

TABLE 4 Storage modulus Rate of Sample No. (MPa)(27° C.) ascent (%) Contrast 3545.4 0.00 sample 2 Contrast 4103.6 15.74 sample 3 Embodiment 4598.86 29.71 sample 1 Embodiment 4782.49 34.89 sample 2 Embodiment 5040.8 42.18 sample 3 Embodiment 5164.5 45.67 sample 4

TABLE 5 Loss modulus Rate of Sample No. (MPa)(27° C.) ascent (%) Contrast 128.97 0.00 sample 2 Contrast 109.88 −14.80 sample 3 Embodiment 158 22.51 sample 1 Embodiment 165 27.94 sample 2 Embodiment 172.36 33.64 sample 3 Embodiment 176.99 37.23 sample 4

The calculation formula of the rate of ascent is equal to [(the numerical values of all samples−the numerical value of the contrast 2)/the numerical value of the contrast 2]*100%.

Table 4 and table 5 show DMA test samples (size: 10 mm*5 mm*1 mm) prepared by pouring each formula resin into the molds (without fiberglass clothes), and then cured in hot oven at 105° C. for 3 hr, after cured, the DMA samples are ground by fine sand papers, an observed storage modulus and the loss modulus obtained by heating up to 150° C. from 0° C. at the vibration frequency of 1 Hz and the heating speed of 2° C./min in an apparatus, and the temperature of the toe cap product is room temperature, so that the value of 27° C. is served as a reference. In the table 4, the storage modulus shows the rigidity of the material, and the loss modules shows the damping capacity or toughness (the capacity of absorbing the energy) of the material. When the unmodified CNT (contrast 3) in the formula, the rigidity is ascended, but the toughness is descended, the material is easily fractured due to the defects generated due to the carbon nanotube aggregation in the resin, and the resin is hard and brittle due to the unmodified CNT according to the data; the rigidities and toughness of the formulas (embodiments 1-4) added with each types of the modified carbon nanotubes can be obviously enhanced, It is a proven fact that the strong bonding of the covalent bond is formed between the modified carbon nanotubes and the resin, so that the high toughness and the high rigidity of the carbon nanotubes can be exerted on the property of the composite. This results can also prove that the modified carbon nanotubes can be uniformly distributed in the resin after being modified (FIGS. 1 (c) and (d)), and no aggregation is formed, so the toughness of composite can be enhanced; according to the above experimental data, when adding 2% of modified CNT, the rigidity and toughness of the resin containing the toughening agents is promoted by 45.67% by the formula (embodiment 4), the toughness can be ascended by 37.23%. The result proves that the excellent mechanical performance of the carbon nanotubes can be fully displayed on the impact resistance and the rigidity of the composite through the specific modification on the surface of carbon nanotubes, and concept of the nanocomposite with a nano reinforcement can be realized.

The above embodiment is only a better scheme of the toe caps, does not limit the toe caps in any way, and is provided with other variants and versions on premise that the technical scheme recorded by the claims is not exceeded. 

What is claimed is:
 1. Safety toe caps made from nano composite material, characterized in that the safety toe caps are made by hand-lay up method providing and pressing a plurality of layers of glass fiber cloth coated with resin paste into a die to form the end product, with the following percentage of the resin paste and the glass fiber cloth by mass: 30-45% of the resin paste and 55-70% of the glass fiber cloth, 100% in total; the resin paste contains the following components in percentage by mass: 30-50% of thermosetting resin, 0.1-5% of modified carbon nanotubes, 10-30% of modified nitrile rubber, 5-25% of polyurethaneacrylate, 1-5% of prepolymerized silane oligomer, 0.5-2% of initiator A (tert-Butyl peroxybenzoate), 1-2% of initiator B (tert-Butyl peroxy-2-ethylhexanoate), 5-20% of low-profile additive, 1-10% of thickener A, 1-3% of thickener B and 2-5% of inner demolding agent.
 2. The safety toe caps made from the nano composite material according to claim 1, characterized in that the glass fiber cloth is a piece of silane-modified alkali-free glass fiber cloth.
 3. The safety toe caps made from the nano composite material according to claim 1, characterized in that the silane-modified alkali-free glass fiber cloth is prepared by immersing a piece of alkali-free glass fiber cloth into 3-8 wt. % solution of silane coupling agent in ethanol, remaining for 10-20 s at 20-25° C., and then taking the alkali-free glass fiber cloth out and drying for 10-12 hrs in nitrogen atmosphere at 90-110° C.
 4. The safety toe caps made from the nano composite material according to claim 1, characterized in that the thermosetting resin is bisphenol A epoxy based vinyl ester resin; the initiator A is tert-Butyl peroxybenzoate; the initiator B is tert-Butyl peroxy-2-ethylhexanoate; the low-profile additive is polycaprolactone; the thickener A is magnesium oxide; the thickener B is magnesium hydroxide; the inner demolding agent is stearic acid zinc.
 5. The safety toe caps made from the nano composite material according to claim 1, characterized in that the preparation of the modified carbon nanotubes comprises the following steps: (1) first, making the carbon nanotubes into a cake shape with 0.5-1 mm in thickness and 0.5-5 cm in diameter, and then immersing the carbon nanotube cakes into the plasma to react for 300-1,200 s to obtain oxidized carbon nanotubes; (2) adding the oxidized carbon nanotubes into a mixture of 95 wt % ethanol and silane coupling agent which are mixed according to a proportion of 50:(1-10) by weight, adjusting pH to 2.5-5.5 with hydrochloric acid, heating for 3-6 hrs at 50-75° C. while passing in nitrogen, washing for 2-4 times with ethanolanhydrous ethanol, and then placing into an oven for drying for 6-8 hrs at 60-80° C. in nitrogen atmosphere.
 6. The safety toe caps made from the nano composite material according to claim 5, characterized in that the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes, and the carbon nanotubes are 10-90 nm in diameter and 5-50 μm in length.
 7. The safety toe caps made from the nano composite material according to claim 5, characterized in that the source gases of plasma is a mixture of 99.995% argon and steam, the steam being 0.5-5% by volume (volume percent); and the frequency of the plasma generator is 13.56 MHz and the RF power is 100-250 W.
 8. The safety toe caps made from the nano composite material according to claim 1, characterized in that the preparation of the modified nitrile rubber comprises the following steps: (1) in parts by weight, uniformly mixing 5-10 parts of methyl acrylic monomer, 50-60 parts of butadiene and 10-40 parts of acrylonitrile to form a mixture, then adding azodiisobutyronitrile (0.5-2% of the weight of the mixture) and tert-dodecylthiol (0.1-1% of the weight of the mixture), stirring constantly after passing in nitrogen, heating to 50-70° C., and reacting for 2-5 hrs at constant temperature to obtain carboxy-terminated butadiene-acrylonitrile; and (2) in parts by weight, mixing 10-25 parts of carboxy-terminated butadiene-acrylonitrile, 100 parts of bisphenol A epoxy based vinyl ester resin, 15-25 parts of methacrylic acid and 1-2 parts of triphenylphosphine, stirring constantly while passing in nitrogen, raising the temperature to 100-150° C., remaining the temperature and reacting for 2-4 hrs, and naturally cooling to room temperature at the end of reaction.
 9. The safety toe caps made from the nano composite material according to claim 1, characterized in that the preparation method of the prepolymerized silane oligomer comprises the following steps: in parts by weight, adding 1-3 parts of 95 wt % ethanol into 2-5 parts of silane coupling agent KH-570(CAS No.:2530-85-0), continuously stirring under the condition that nitrogen is supplied, raising the temperature to be 60-80° C., keeping the temperature and reacting for 2-5 hours, and finally ethanol was evaporated under reduced pressure.
 10. A preparation method of the safety toe caps made from the nano composite material, characterized by comprising the following steps: uniformly mixing up components of the resin paste according to a ratio, subsequently uniformly coating the mixture on a single layer of glass fiber cloth, subsequently respectively covering a layer of PE film on the upper and lower surfaces of the glass fiber cloth coated with the resin paste, then rolling through a roller to obtain a sheet material, aging for 20-28 hours at 35-45° C., cutting the perpreg in designed shape, tearing off the PE films, stacking the cut prepreg into pre-formed toe caps by using a hand layer-up method, subsequently hot-pressing for 150-250 seconds in the fixed mold in a hot-pressing machine in the pressure of 30-45 MPa at 135-155° C. to form, demolding, and subsequently grinding and trimming to obtain a product. 